Standard ballscrew kits use 5/8" Thomson ballscrews with a .200 pitch. Here is a link to the Thomson catalog page with detailed information on the ballscrews. See page 237 for backlash info

X1 Micro-Mill CNC kit now available!

X2 Mini-Mill kits now available!

CNC kits for the Sieg X1 type Micro mill. Just go to the
Micro Mill section for details.
These kits use strong one peice motor mounts for rigidity, and no machine modifications
are required to install the kit.
All kits include thrust bearings too.

CNC kits for Sieg X2 mini mill based machines.. There are photos of the complete kits for the mini mill online. Click on details and then the photos link to see them. Check out the videos of the mini mill too.